in Advanced Delphi :: Simply speaking, decompilation is the inverse of compilation: translating an executable file into a higher level language. Suppose you lose your Delphi project's source and you only have the executable file: reverse engineering (decompilation) is useful if the original sources are not available.
Hm, "sources not available", does this mean that we can decompile other people's Delphi projects? Well, yes and no..

Read the full article to learn how to Decompile a Delphi application.

Related:

• Embeding Resources in Delphi program's EXE
• Dynamic Link Libraries (DLL) and Delphi
• Free Source Delphi Code Projects

in Vigenere Cipher :: A long time Delphi developer, Alan Lloyd had a few comments on the recently published Vigenere Cipher - Delphi Implementation - Fancy Delphi Application Contest Entry #49.

Alan suggests:

While we have loads of computation power & memory available today, I think as a professional it is better to code quicker than slower, unless it makes code unclear.

In the posted Vigenere code . . .

1. String memory allocation/re-allocation is slow so avoid ConCat(), String + String (even though its quicker than ConCat), and Delete(). Better to SetLength for strings and use index accessing for characters.
2. Use 'for' loops rather than 'while' loops.
3. Reduce the code for every character. Check for bEncrypt before entering repeated similar code in a 'for' loop for each character action.
4. IMO sTable should be initialised before use by := '' or SetLength(). AIUI variables in functions are not zeroed, and you might be using garbage.
5. Crypt by re-referencing the key as given rather that using multiple keys up to the source length.

Here's the Vigenere crypto algorithm as suggested by Allan:

function Vigenere(Src, Key : string; Encrypt : boolean) : string;
const
  OrdMinChar : integer = Ord('A');
  OrdMaxChar : integer = Ord('Z');
  IncludeChars : set of char = ['A'..'Z'];
var
  CharRangeCount, i, j, KeyLen, KeyInc, SrcOrd, CryptOrd : integer;
  SrcA : string;
begin
  CharRangeCount := OrdMaxChar - OrdMinChar + 1;
  KeyLen := Length(Key);
  SetLength(SrcA, Length(Src));
  If Encrypt then 
  begin
    // transfer only included characters to SrcA for encryption
    j := 1;
    for i := 1 to Length(Src) do
      begin
      if (Src[i] in IncludeChars) then 
      begin
        SrcA[j] := Src[i];
        inc(j);
      end;
    end;
    SetLength(SrcA, j - 1);
  end;
  SetLength(Result, Length(SrcA));
  if Encrypt then
    begin
    // Encrypt to Result
    for i := 1 to Length(SrcA) do 
    begin
      SrcOrd := Ord(Src[i]) - OrdMinChar;
      KeyInc := Ord(Key[((i - 1 ) mod KeyLen)+ 1]) - OrdMinChar;
      CryptOrd := ((SrcOrd + KeyInc) mod CharRangeCount) + OrdMinChar;
      Result[i] := Char(CryptOrd);
    end;
  end;
  else
  begin
    // Decrypt to Result
    for i := 1 to Length(SrcA) do 
    begin
      SrcOrd := Ord(Src[i]) - OrdMinChar;
      KeyInc := Ord(Key[((i - 1 ) mod KeyLen)+ 1]) - OrdMinChar;
      CryptOrd := ((SrcOrd - KeyInc + CharRangeCount) mod CharRangeCount) + OrdMinChar;
      // KeyInc may be larger than SrcOrd
      Result[i] := Char(CryptOrd);
    end;
  end;
end;

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in FDAC :: Vigenere coding is one of the most ancient forms of cryptography. In a Vigenere cipher, messages are encoded by mapping letters to numeric values and adding the plaintext values to the keytext values, modulo the number of letters in the alphabet.

Interested in how to implement Vigenere cipher in Delphi?

This is the 49th entry to the Fancy Delphi Application Contest

Read the full article to find more about (+ download source code) Vigenere Cipher Delphi Implementation

When you download the application and test, rate it:

1. Excellent
2. Superb
3. Good
4. Average
5. Poor

If you already voted, take a look at poll results.

Related:

• File Encrypt / Decrypt
• Protect your Delphi Software
• String Handling Routines